On this day, April 25, in 1929, the world learned how astronomer Edwin Hubble had discovered that the universe was much larger than we had believed. On this day in 2025, you can preorder a book and on the 29th learn about this and four other Astrophysics discoveries that changed how we see the universe — and ourselves — in The Story of Astrophysics in Five Revolutions.
By Ersilia Vaudo, translated by Vanessa Di Stefano. If you use this link we get a penny or something.
He had published his seminal paper in the March issue of Astrophysical Journal but on April 25th in Proceedings of the National Academy of Sciences he published the how, and people began to think about what it meant. He had discovered that the collection of gas and dust we call Andromeda was actually another galaxy.